This invention relates to a pressure limiter valve for use in the control of inflating and deflating the deicer pad of an airfoil utilizing low pressure unregulated air.
Under certain atmospheric conditions, ice will form and accumulate on the leading edge of an aircraft wing, struts, stabilizers and propellers. In the discussion hereinafter reference to these parts will be made as airfoil and the description will be directed to the wing of an airplane, it being understood that such description is equally applicable to the aircraft struts, stabilizers or propellers. A deicer pad is the inflatable and resilient extensible units mounted on the leading edge of the airfoil and its repeated inflation and deflation prevents the accumulation of ice on the airfoil. Such accumulation of ice is undesirable as it adds weight to the aircraft as well as alters the aerodynamics configurations of the airfoil to change materially the efficiency thereof.
To break up the ice formation on the wings of an aircraft, pneumatic deicing equipment such as deicer pads or boots are employed utilizing a series of resilient inflatable tubes covering the leading edge area of the wings to deice them. An air supply system is used to alternately inflate and deflate the tubes to flex the deicer pad. Such repetitive flexing action shatters or breaks up the ice formation or layers as they form on the leading edge of the deicer pad and are broken into particles, which ice particles are blown off by the airstream moving over the airfoil.
Since icing conditions exist only for a relatively small portion of the total aircraft flight time it is necessary during non-deicing use to maintain a vacuum on the tubes to assure a smooth exterior surface on the deicing pad. Irregularities on the deicer pad would seriously reduce aircraft performance and efficiency by creating unwanted air turbulence. To effect a positive pressure into the tubes of the deicer pad, a solenoid operated valve upon actuation is operative to direct pressurized air thereto in cooperation with a pressure regulator which is used to maintain a predetermined air pressure to the deicer system. Under normal conditions the air supply for the deicer is the bleeding off of a very small portion of the pressurized air from the compressor section of the aircraft's turbine engine. Under certain operating conditions, the bleed off pressure can drop to a pressure equal to or slightly less than the deicer system value. As the supply pressure drops to pressures lower than the needed pressure, the pressure regulator becomes restricted and the deicer inflation flow of air is reduced substantially and impairs the proper functioning of the deicer pad. The present invention is directed to the elimination of the need for a pressure regulator and thus in effect uses unregulated air pressure to insure the proper functioning of the deicer by utilizing the available source of air pressure to inflate the pneumatic deicer rapidly, especially when the source pressure is near deicer operating pressure. The pressure limiter of the present invention overcomes the limitation of present pneumatic deicer systems operating components that result in deicer inflation that is too slow for effective performance when the air supply pressure is low in the turbine engine's bleed system. Such pressure limiter valve utilizes all available source of air pressure and flow to inflate pneumatic de-icers rapidly, especially when the source pressure is near de-icer operating pressure. Such pressure valve is particularly useful as it eliminates the need for a pressure regulator.